1. Field of the Invention
The present invention relates to a method of producing a functional polymer particle.
2. Description of the Related Art
Conventionally, polymer particles having a particle diameter in the range of about 0.01 to 50 μm are useful as spacers, standard particles, particles for examination of antigen-antibody reaction, catalyst particles, particles for combinatorial chemistry, toner additives, cosmetic additives, rheology controlling agents, low profile additives, improvers for resin mechanical properties, antiblocking agents for resin film, film lubricants, running stabilizers for thermoseisitive paper, etc. and are used in various fields. In recent years, the performance required of fine resin particles varies widely from the type of functional groups in the particles, the shape of the particles, the uniformity of particle diameters, the strength of the particles, heat resistance, etc.
In particular, there is great demand for the uniformity of particle diameters. For example, fine resin particles are often used as spacers in a liquid crystal display panel, to maintain a constant clearance between two glass substrates constituting the panel. However, if the particle size distribution of the fine particles is broad, spacer particles having particle diameters smaller than the central particle diameter move and easily become unevenly distributed in the space between the two glass substrates. Further, another problem occurs, in that spacer particles larger than the central particle diameter are easily destroyed. Accordingly, fine resin particles having a narrow distribution of particle diameters are required.
The polymer particles having particle diameters in such a range can be produced usually by granulation in an aqueous solvent according to an emulsion polymerization method or a suspension polymerization method. As the method of producing particles containing an hydrophilic group such as an amino group, a hydroxyl group and a carboxyl group, a method of emulsion polymerization or suspension polymerization using a polymerizable monomer containing a hydrophilic group can be mentioned as a first method. A method of granulating a polymerizable monomer having a hydrophilic group, to which a protective group is attached, through emulsion polymerization or suspension polymerization and then eliminating the protective group can be mentioned as another method of producing particles containing hydrophilic groups. In the first method, however, the polymerizable monomer is hydrophilic, and thus a proportion of the hydrophilic monomer in the resulting hydrophilic monomer-hydrophobic monomer copolymer can be lower than the proportion of the hydrophilic monomer in the starting materials charged, and further the yield is reduced. In the other method, even if particles having the same composition as in the starting materials can be produced in high yield, a procedure, which eliminate the protective group, is later required.
Moreover, in cases in which the polymerizable monomer, having a hydrophilic group, to which a protective group is attached, is not commercially available, a synthesis attaching the protective group to the hydrophilic group must be performed. The steps for this synthesis are numerous and are not simple. Thus increasing the steps and making the another method difficult (Japanese Patent Application Laid-Open (JP-A) No. 2-166102). In JP-A No. 58-219455, emulsion polymerization is carried out using persulfate as an initiator, to introduce a functional group into a catalytic fragment in the resulting polymer. In this method, however, particles having a large diameter cannot be obtained, and introduction of many functional groups is difficult. In JP-A No. 5-216049, after particles (seed particles) are prepared by suspension polymerization, polymerizable monomers having functional groups are absorbed into the particles, and seed polymerization is performed to produce particles having the functional groups, which were introduced thereinto. However, when the particles are produced by suspension polymerization, it is difficult to obtain particles of the desired particle diameter with a good particle size distribution, so a classification procedure is required to obtain particles of narrow particle size distribution, thus reducing the yield. Further, there is a disadvantage that at the time of seed polymerization, unabsorbed polymerizable monomers can form undesired fine particles, or swollen particles might aggregate to form coarse particles, and broaden the particle size distribution.
In JP-A No. 63-90521, a polymerizable monomer having an active functional group is used to produce particles by dispersion polymerization. However, this prior art literature describes the particle diameter but does not describe the particle size distribution thereof. In JP-A No. 64-33111, a polymerizable monomer having an active functional group and a crosslinking polymerizable monomer are subjected to dispersion polymerization to produce particles. However, as the ratio of the crosslinking monomer is increased, the stability of the polymerization reaction system is greatly deteriorated, thus making it difficult to produce particles of a narrow particle size distribution with the desired particle diameter. Further, there was the problem of a reduction in the reactivity of the active functional group in the crosslinked particles. Conventionally, it has been difficult to produce polymer particles having a hydrophilic functional group with a good particle size distribution by an easy process.